Officers in London were ­ inquiring into allegations made by a teenage rent boy that a Cabinet minister had been abusing him.

The youth claimed to be one of a number of boys regularly having sex with rich and powerful men in the 1980s – some of whom would fly to the illegal orgies from Europe.

As well as the Cabinet minister – who is still alive – he pointed the finger at judges, European bigwigs and senior civil servants.

He told his story to detectives, who are understood to have received other allegations against the minister.

But a former detective who worked on the case revealed they were ­suddenly told to halt the probe.

The furious ex-policeman said: “It wasn’t that we ran out of leads but it reached a point where a warning to stop came.

“It was a case of ‘get rid of everything, never say a word to anyone’. It was made very clear to me that to ­continue asking questions would ­jeopardise my career.”

There is no suggestion that Mrs Thatcher – who is now 87 and suffering from dementia – knew about the ­investigation or the fact it was stopped.

As Britain’s first female PM, she held power from 1979 until 1990.

The accused top Tory was never arrested and no one was ever charged over the rent-boy ring.

The vulnerable teen who spoke to ­detectives vanished just weeks after blowing the whistle.

The dropped probe was carried out by the Metropolitan Police – the same force now investigating six decades of abuse by telly star Jimmy Savile. It ­discovered high-profile men were ­paying the boys to attend sex parties at “millionaire properties” in London and the Home Counties.

A “network” of boys, including ­runaways, were used – many of whom were said to have been recruited around the then notorious rent-boy haunt of Leicester Square.

Some of the VIPs were said to have flown in via RAF Northolt on the outskirts of London.

One boy told police wealthy men from Belgium attended the parties, which were described as “high class” and featured top-notch food and booze.

The detective said the whistleblower was petrified about the repercussions.

He said: “The boys had been trapped in a cycle and were scared stiff about what might happen if they were found to have spoken.” The married Cabinet minister the boy named held a series of high-level posts in government.

A Whitehall security source said he received extra vetting from MI5 prior to taking up high office after rumours about his private life.

“The security services looked at him with special care,” the source said. “When you are nominated for a key Cabinet post it doesn’t matter what background you are from, you have to be vetted.

“Any weaknesses have to be disclosed to the Cabinet Secretary and Prime Minister

“But suspicions are not evidence. He’s a clever man – he would have ­dismissed it with a laugh.

“Mrs Thatcher may have suspected he was bisexual but that’s not a crime.”

Police sources in the minister’s home region said there are other unsubstantiated allegations that he was once found trying to abuse the son of a friend.

Last week Labour MP Tom Watson said he had been told of evidence ­linking another child sex ring to ­Parliament and Downing Street.

He said case files from 20 years ago involving convicted paedophile Peter Righton contained evidence of links to Number 10.

He said there was “clear intelligence of a widespread paedophile ring”, ­adding: “One of its members boasts of his links to a senior aide of a former Prime Minister, who says he could smuggle indecent images of children from abroad.”

Mr Watson said the leads were not followed up. And he said he had been contacted by someone who claimed the police “held a vast quantity of ­material suggesting Jimmy Savile was a ­predatory paedophile”.

Last week it emerged at least seven police investigations into Savile while he was alive did not result in charges.

Scotland Yard, now probing the claims of up to 300 victims, investigated the TV presenter in the 1980s over claims he attacked a girl in a caravan at BBC Television Centre in London.

Last week we asked Scotland Yard about the dropped investigation into the Cabinet minister in the 1980s at the time of going to press they had not ­responded.